A hydraulic shovel, as a type of construction machine, generally comprises a lower travel structure, an upper swing structure which is mounted on the lower travel structure to be capable of swiveling, and a multijoint work implement (including a boom, an arm and a bucket) which is connected to the upper swing structure to be capable of increasing/decreasing its elevation angle. A hydraulic driving device for the hydraulic shovel includes, for example, a hydraulic pump which is driven by the engine, a plurality of hydraulic actuators (specifically, traveling hydraulic motors, a boom hydraulic cylinder, an arm hydraulic cylinder, a bucket hydraulic cylinder, etc.) which are driven by hydraulic fluid from the hydraulic pump, and a control valve which controls the flow of the hydraulic fluid from the hydraulic pump to the hydraulic actuators in response to the operator's operation on controller devices.
An engine-powered hydraulic shovel is equipped with only an engine as the power source for the hydraulic pump. Among such engine-powered hydraulic shovels, some types of mini-shovels suitable for operations in small or restricted worksites, called “minimal tail swing radius type” or “minimal swing radius type”, are known (see Patent Literatures 1 and 2, for example). A minimal tail swing radius mini-shovel described in the Patent Literature 1 has the work implement connected to the front of the upper swing structure via a swing post and is designed so that the swing radius (turning radius) of the rear end of the upper swing structure substantially fits in the overall width of the lower travel structure. In a minimal swing radius mini-shovel described in the Patent Literature 2, the work implement is connected to a part of the upper swing structure closer to its swiveling center so that the upper swing structure with the work implement can swing substantially within the overall width of the lower travel structure.
In the mini-shovels described in the Patent Literatures 1 and 2, the upper swing structure includes a swiveling frame which forms the substructure of the upper swing structure, a counter weight which is provided at a rear end position on the swiveling frame to cover the rear of the engine arranged on the swiveling frame, a floor member which is mounted on the swiveling frame to extend substantially across the total length of the swiveling frame in its longitudinal direction and which includes a floor plate serving as the foothold for the operator and a cab seat pedestal extending upward from the rear of the floor plate to overhang rearward and cover the front and top of the engine, and a support member which is mounted on the swiveling frame to extend over components such as the engine and support a rear part of the floor member. In short, due to the restriction on the dimensions of the upper swing structure in horizontal directions, the cab is formed on the floor member, the engine room (machine room) is formed to be separated from the cab by the cab seat pedestal of the floor member (i.e., to get into the space under the rear part of the floor member), and the engine, etc. are arranged in the engine room.
The engine is mounted transversely (to extend in the transverse direction) and is supported by support brackets and vibration-proof mounts. The left-hand end of the output shaft of the engine is coaxially connected to the input shaft of the hydraulic pump so that the hydraulic pump is integrally combined with the engine. The right-hand end of the output shaft of the engine is connected to the rotating shaft of a cooling fan via a power transmission mechanism (specifically, pulleys, fan belt, etc.). Heat exchangers such as a radiator and an oil cooler are arranged to the right of the cooling fan. Tanks such as a fuel tank and a hydraulic fluid tank are arranged in front of the heat exchangers (i.e., to the right of the floor member). Further, a control valve (control valve unit) is arranged under the floor plate of the floor member.
Incidentally, hybrid hydraulic shovels equipped with a generator/motor (rotating electric machine) are being proposed in recent years (see Patent Literature 3, for example) from the viewpoints of increasing the fuel efficiency, improving the exhaust gas characteristics, reducing the noise, etc. In the hybrid hydraulic shovel described in the Patent Literature 3, the rotating shaft of the generator/motor is connected to the output shaft of the engine and the input shaft of the hydraulic pump via a gear mechanism. The generator/motor has both the function of an electric generator which is driven by the output power of the engine and thereby generates electric power and the function of an electric motor which is driven by electric power from a battery and thereby serves as an auxiliary power source for the hydraulic pump.